On 3 December 2013 04:42, Andrew Barnert <abarnert@yahoo.com> wrote:
Shouldn't this be tied to ABCs rather than redesigning and reimplementing most of ABC to add a little bit on top?
This seems like an apropos place for this link: http://docs.python.org/3/library/abc#abc.ABCMeta.__subclasshook__ That's the existing "formalised ducktyping" hook, that already allows things like the following:
class MyClass: ... def __len__(self): ... return 0 ... from collections.abc import Sized isinstance(MyClass(), Sized) True issubclass(MyClass, Sized) True
The advantage ABCs have over ducktyping alone is that subclassing and explicit registration allow ambiguities like the one between the Sequence and Mapping interfaces to be resolved (you can't always just ducktype those, as they have the same methods - they differ only in how the __*item__ methods handle slice objects). Cheers, Nick. -- Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia